Method of user equipment monitoring control information in a multiple node system and user equipment using the method

ABSTRACT

There are provided a method of user equipment monitoring control information and user equipment using the method. The method includes receiving information about a first reference position for a first Enhanced-Physical Control Format Indication Channel (E-PCFICH) from a Base Station (BS); detecting the first E-PCFICH in a resource indicated by the information about the first reference position; obtaining information about a reference position for a second E-PCFICH based on the information about the first reference position, wherein each of the first E-PCFICH and the second E-PCFICH is a control channel including information about the size of the frequency domain for an Enhanced-Physical Downlink Control Channel (E-PDCCH) for demodulating the control information by using a UE-specific Reference Signal (URS); and detecting the second E-PCFICH based on the obtained information about the reference position for the second E-PCFICH.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application is a National Stage entry under U.S.C.§371 of International Application No. PCT/KR2012/005543 filed on Jul.12, 2012, which claims the benefit of U.S. Provisional Application No.61/506,643 filed on Jul. 12, 2011. The entire contents of all of theabove applications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to wireless communication and, moreparticularly, to a method of user equipment monitoring for controlinformation in a multi-node system and a user equipment using the same.

BACKGROUND ART

Recently, the data transfer rate over a wireless communication networkis rapidly increasing. This results from the appearance and spread of avariety of devices, such as smart phones and tablet PCs which requireMachine-to-Machine (M2M) communication and a high data transfer rate. Inorder to meet a higher data transfer rate, Carrier Aggregation (CA)technology and Cognitive Radio (CR) technology for efficiently usingmore frequency bands and multiple antenna technology and multiple basestation cooperation technology for increasing the data capacity within alimited frequency are recently are highlighted.

Furthermore, a wireless communication network is evolving toward atendency that the density of accessible nodes around a user isincreasing. Here, the term ‘node’ may mean antennas or a group ofantennas which are spaced apart from one another in a DistributedAntenna System (DAS). However, the node is not limited to the meaning,but may be used as a broader meaning. That is, the node may become apico eNB (PeNB), a home eNB (HeNB), a Remote Radio Head (RRH), a RemoteRadio Unit (RRU), a relay, or distributed antennas (or group). Awireless communication system including nodes having a high density mayhave higher system performance through cooperation between nodes. Thatis, if the transmission and reception of each node are managed by onecontrol station and thus the node is operated like an antenna or anantenna group for one cell, the nodes may have much more excellentsystem performance as compared with the case where the nodes areoperated as independent base stations without cooperation. A wirelesscommunication system, including a plurality of nodes and a base stationfor controlling a plurality of nodes, is hereinafter referred to as amulti-node system.

In a multi-node system, it may be necessary to send control informationthrough radio resources distinguished from each other for each node. Inthis case, in order to correctly decode control information in radioresources through which the control information is transmitted,information about reference position and the size of radio resources mayneed to be informed. If there is a plurality of radio resources within asubframe, however, there is a problem in that to signalize informationabout the reference position and size of each radio resourceindividually has great overhead.

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a method of userequipment monitoring control information in a multi-node system and userequipment using the same.

Solution to Problem

In an aspect, a method of User Equipment (UE) monitoring controlinformation is provided. The method comprises: receiving informationabout a first reference position for a first Enhanced-Physical ControlFormat Indication Channel (E-PCFICH) from a Base Station (BS); detectingthe first E-PCFICH in a resource indicated by the information about thefirst reference position; obtaining information about a referenceposition for a second E-PCFICH based on the information about the firstreference position, wherein each of the first E-PCFICH and the secondE-PCFICH is a control channel comprising information about a size of afrequency domain for an Enhanced-Physical Downlink Control Channel(E-PDCCH) for demodulating control information by using a UE-specificReference Signal (URS); and detecting the second E-PCFICH based on theobtained information about the reference position for the secondE-PCFICH.

The method may further comprise: obtaining a frequency size of a firstE-PDCCH region through the first E-PCFICH and obtaining a frequency sizeof an second E-PDCCH region through the second E-PCFICH; and searchingthe first E-PDCCH region and the second E-PDCCH region for the E-PDCCHfor the UE.

The method may further comprise: receiving information about a referenceposition for the first E-PDCCH indicating a Resource Block (RB) wherethe first E-PDCCH region is started.

An RB where the second E-PDCCH region is started may be determined basedon the information about the reference position for the first E-PDCCH.

When the first E-PCFICH and the second E-PCFICH are mixed in one or moreidentical RBs, the information about the first reference position mayindicate a first RB of the one or more RBs.

The method may further comprising: receiving information about a totalnumber of a plurality of E-PCFICHs when the plurality of E-PCFICHs ismixed in the one or more identical RBs.

The information about the first reference position may be receivedthrough a higher layer signal.

In another aspect, user equipment(UE) is provided. The UE comprises: aRadio Frequency (RF) unit configured to transmit and receive radiosignals; and a processor connected to the RF unit, wherein the processoris configured to: receive information about a first reference positionfor a first Enhanced-Physical Control Format Indication Channel(E-PCFICH) from a Base Station (BS); detect the first E-PCFICH in aresource indicated by the information about the first referenceposition; obtain information about a reference position for a secondE-PCFICH based on the information about the first reference position,wherein each of the first E-PCFICH and the second E-PCFICH is a controlchannel comprising information about a size of a frequency domain for anEnhanced-Physical Downlink Control Channel (E-PDCCH) for demodulatingthe control information by using a UE-specific Reference Signal (URS);and detect the second E-PCFICH based on the obtained information aboutthe reference position for the second E-PCFICH.

The processor may obtain a frequency size of a first E-PDCCH regionthrough the first E-PCFICH, obtain a frequency size of an second E-PDCCHregion through the second E-PCFICH, and search the first E-PDCCH regionand the second E-PDCCH region for the E-PDCCH for the user equipment.

The process may receive information about a reference position for thefirst E-PDCCH indicating a Resource Block (RB) where the first E-PDCCHregion is started.

An RB where the second E-PDCCH region is started may be determined basedon the information about the reference position for the first E-PDCCH.

When the first E-PCFICH and the second E-PCFICH are mixed in one or moreidentical RBs, the information about the first reference position mayindicate a first RB of the one or more RBs.

The processor may further receive information about a total number of aplurality of E-PCFICHs when the plurality of E-PCFICHs is mixed in theone or more identical RBs.

The information about the first reference position may be receivedthrough a higher layer signal.

Advantageous Effects of Invention

In accordance with the present invention, when a plurality of resourceregions through which control information is transmitted to userequipment for each node is supported in a multiple node system, eachnode or base station can inform the user equipment of the referenceposition of the resource regions with small signaling overhead. The userequipment can know a reference position for another control channelbased on information about a reference position for a specific controlchannel.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of a multi-node system;

FIG. 2 shows the structure of a radio frame in 3GPP LTE;

FIG. 3 shows an example of a resource grid for one slot;

FIG. 4 shows the structure of an uplink subframe;

FIG. 5 shows the structure of a downlink subframe;

FIG. 6 is a block diagram showing a process of generating a PDCCH;

FIG. 7 shows an example of the resource mapping of a PDCCH;

FIG. 8 is an exemplary diagram showing a common search space and aUE-specific search space for the monitoring of PDCCHs;

FIG. 9 shows an example in which a reference signal is mapped in adownlink subframe;

FIG. 10 shows an example in which information about the size of a PDCCHis received using a PCFICH;

FIG. 11 shows an example of an R-PDCCH;

FIG. 12 shows an example in which E-PDCCHs are allocated and an exampleof scheduling through the E-PDCCHs;

FIG. 13 shows an example of a node-specific E-PDCCH region;

FIG. 14 shows an example in which an E-PCFICH is placed in RBs that forman E-PDCCH region;

FIG. 15 shows an example in which an E-PCFICH is placed in some resourceelements within RBs that form an E-PDCCH region;

FIG. 16 shows an operation of UE according to an embodiment of thepresent invention; and

FIG. 17 is a block diagram showing of a BS and UE.

MODE FOR THE INVENTION

The following technology may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), andSingle Carrier-Frequency Division Multiple Access (SC-FDMA). CDMA may beimplemented using radio technology, such as Universal Terrestrial RadioAccess (UTRA) or CDMA2000. TDMA may be implemented using radiotechnology, such as Global System for Mobile communications(GSM)/General Packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented using radio technology, suchas IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or EvolvedUTRA (E-UTRA). IEEE 802.16m is the evolution of IEEE 802.16e, and itprovides backward compatibility with systems based on IEEE 802.16e. UTRAis part of a Universal Mobile Telecommunications System (UMTS). 3^(rd)Generation Partnership Project (3GPP) Long Term Evolution (LTE) is partof an Evolved UMTS (E-UMTS) using E-UTRA, and it adopts OFDMA indownlink and adopts SC-FDMA in uplink. LTE-Advanced (LTE-A) is theevolution of LTE.

In order to classify a description, the present invention is assumed tobe applied to an LTE-A system, but the technical spirit of the presentinvention is not limited thereto.

FIG. 1 shows an example of a multi-node system.

The multi-node system includes a Base Station (BS) and a plurality ofnodes.

The BS provides communication service to a specific geographical area.The BS commonly refers to a fixed station that communicates with UserEquipments (UEs), and it may also be called another terminology, such asan evolved-NodeB (eNB), a Base Transceiver System (BTS), or an AdvancedBase Station (ABS).

FIG. 1 shows distributed antennas as an example of nodes. However, thenodes are not limited to the distributed antennas, but may beimplemented using, for example, a macro BS, a picocell BS (PeNB), a homeBS (HeNB), a Remote Radio Head (RRH), a relay. The nodes are also calledpoints. The nodes may be connected to the BS and may be controlled ormanaged by the BS.

From a viewpoint of UE, a node may be identified or indicated through aReference Signal (RS) or a pilot signal. The RS (hereinafter also calleda pilot signal) refers to a signal known by both a transmission terminaland a reception terminal, and it is used for channel measurement anddata demodulation. The RS may include, for example, a Channel StatusIndication-Reference Signal (CSI-RS) defined in 3GPP LTE-A, a preambledefined in IEEE 802.16m, and a midamble. The RS or a configuration forthe RS may be mapped to each node (or the transmit antenna of eachnode). If information about mapping between an RS configuration and anode is given to UE or UE previously knows the mapping information, theUE may identify the node or may be informed of the node based on theCSI-RS configuration and may calculate channel status information aboutthe node. The RS configuration may include pieces of information about aconfiguration index, the number of antenna ports of each node, ResourceElements (REs) being used, and an offset about a transport period and atransport time. Accordingly, in this specification, technology in whichUE measures a signal or generates channel status information for aspecific node may mean that a signal for a specific RS is measured orchannel status information is generated from a viewpoint of UE, forconvenience of description.

Referring to back to FIG. 1, the nodes are connected to the BS in awired/wireless manner. Each of the nodes may include one antenna or aplurality of antennas (i.e., an antenna group). Antennas belonging toone node are placed within several meters geographically, and may havethe same characteristics. In a multi-node system, a node may function asan Access Point (AP) accessible to UE.

If the nodes consist of antennas as described above, this multi-nodesystem is also called a Distributed Antenna System (DAS). That is, theDAS refers to a system in which the antennas (i.e., the nodes) aregeographically distributed and placed in various positions and theantennas are managed by a BS. The DAS differs from a conventionalCentralized Antenna System (CAS) in that the antennas of a BS areconcentrated and placed at the center of a cell.

Here, the meaning that the antennas are geographically distributed andplaced may mean that one receiver and a plurality of antennas arearranged so that a difference in the channel status between each of theantennas and the receiver is a specific value or higher when thereceiver receives the same signal from the plurality of antennas. Themeaning that the antennas are concentrated and placed may mean that theantennas are densely placed so that a difference in the channel statusbetween each antenna and one receiver is less than a specific value. Thespecific value may be determined in various ways depending on thefrequency and the type of service used in antennas.

In general downlink refers to communication from a BS or a node to UE,and uplink refers to communication from UE to a BS or a node.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

Referring to FIG. 2, the radio frame includes 10 subframes, and each ofthe subframes includes 2 slots. The slots within the radio frame aregiven slot numbers from #0 to #19. The time that one subframe is takento be transmitted is called a Transmission Time Interval (TTI). The TTImay be called a scheduling unit for data transmission. For example, thelength of one radio frame may be 10 ms, the length of one subframe maybe 1 ms, and the length of one slot may be 0.5 ms.

The structure of the radio frame is only an example. Accordingly, thenumber of subframes included in the radio frame or the number of slotsincluded in the subframe may be changed in various ways.

FIG. 3 shows an example of a resource grid for one slot.

A slot includes a downlink slot and an uplink slot. The downlink slotincludes a plurality of OFDM symbols in the time domain and includesN_(RB) Resource Blocks (RBs) in the frequency domain. The OFDM symbolmay also be called an SC-FDMA symbol depending on a transmission method.The RB is a resource allocation unit, and it includes one slot in thetime domain and a plurality of contiguous subcarriers in the frequencydomain. The RB includes a Virtual Resource Block (VRB), that is, alogical allocation unit, and a Physical Resource Block (PRB), that is, aphysical allocation unit. The VRB and the PRB have the same size, butthe index of the VRB and the index of the PRB may not be identical witheach other.

The number N_(RB) of RBs included in a downlink slot depends on adownlink transmission bandwidth configured in a cell. For example, in anLTE system, the number N_(RB) may be any one of 6 to 110. An uplink slotmay also have the same structure as a downlink slot.

An element on a resource grid is called a Resource Element (RE). The REon the resource grid may be identified by an index pair (k,l) within aslot. Here, k (k=0, . . . , N_(RB)×12−1) is a subcarrier index withinthe frequency domain, and l (l=0, . . . , 6) is an OFDM symbol indexwithin the time domain.

One RB is illustrated as including 7×12 REs including 7 OFDM symbols inthe time domain and 12 subcarriers in the frequency domain but thenumber of OFDM symbols and the number of subcarriers within the RB arenot limited thereto. The number of OFDM symbols and the number ofsubcarriers may be changed in various ways depending on the length of aCP and frequency spacing. For example, in case of a normal CP, thenumber of OFDM symbols may be 7 and in case of an extended CP, thenumber of OFDM symbols may be 6. In one OFDM symbol, the number ofsubcarriers may be one of 128, 256, 512, 1024, 1536, and 2048.

FIG. 4 shows the structure of an uplink subframe.

The uplink subframe may be divided into a control region and a dataregion in the frequency domain. A Physical Uplink Control Channel(PUCCH) on which uplink control information will be transmitted isallocated in the control region, and a Physical Uplink Shared Channel(PUSCH) on which data will be transmitted is allocated in the dataregion. UE may do not send a PUCCH and a PUSCH at the same time or maysend a PUCCH and a PUSCH at the same time depending on a configuration.

A PUCCH for one UE is allocated in the form of an RB pair in a subframe.RBs belonging to an RB pair occupy different subcarriers in a first slotand a second slot. A frequency occupied by RBs belonging to an RB pairallocated to a PUCCH is changed on the basis of a slot boundary. This iscalled that the RB pair allocated to the PUCCH has been subject tofrequency-hopped in the slot boundary. UE may obtain a frequencydiversity gain by sending pieces of uplink control information throughdifferent subcarriers over time.

The pieces of uplink control information transmitted on the PUCCHinclude Hybrid Automatic Repeat request (HARM) Acknowledgement(ACK)/Non-acknowledgement (NACK), Channel State Information (CSI)indicating a downlink channel status, and a Scheduling Request (SR),that is, an uplink radio resource allocation request. The CSI includes aPrecoding Matrix Index (PMI) indicating a precoding matrix, a RankIndicator (RI) indicating a rank value preferred by UE, and a ChannelQuality Indicator (CQI) indicating a channel status.

A PUSCH is mapped to an Uplink Shared Channel (UL-SCH), that is, atransport channel. Uplink data transmitted on the PUSCH may be atransport block, that is, a data block for an UL-SCH transmitted for aTTI. The transport block may be user information. Alternatively, theuplink data may be multiplexed data. The multiplexed data may be themultiplexing of a transport block and control information for an UL-SCH.For example, control information multiplexed with data may include aCQI, a PMI, an HARQ ACK/NACK, and an RI. Alternatively, uplink data mayconsist of only control information.

FIG. 5 shows the structure of a downlink subframe.

The downlink subframe includes two slots in the time domain, and each ofthe slots includes 7 OFDM symbols in a normal CP. A maximum of former 3OFDM symbols of a first slot within the downlink subframe (i.e., amaximum of 4 OFDM symbols for a 1.4 MHz bandwidth) corresponds to acontrol region in which control channels are allocated. The remainingOFDM symbols correspond to a data region in which Physical DownlinkShared Channels (PDSCHs) are allocated. The PDSCH means a channel onwhich a BS or a node sends data to UE.

The control channels transmitted in the control region includes aPhysical Control Format Indicator Channel (PCFICH), a PhysicalHybrid-ARQ Indicator Channel (PHICH), and a Physical Downlink ControlChannel (PDCCH).

A PCFICH transmitted in the first OFDM symbol of the downlink subframecarries a Control Format Indicator (CFI), that is, information about thenumber of OFDM symbols (i.e., the size of the control region), that isused to send control channels in the subframe. UE receives a CFI on aPCFICH and then monitors PDCCHs. Unlike the PDCCH, the PCFICH istransmitted through fixed PCFICH resources of a subframe without usingblind decoding.

A PHICH carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for an uplink HybridAutomatic Repeat Request (HARQ). An ACK/NACK signal for uplink data on aPUSCH transmitted by UE is transmitted on a PHICH.

Control information transmitted through a PDCCH is called DownlinkControl Information (DCI). DCI may include information about theresource allocation of a PDSCH (this is also called a downlink (DL)grant), the resource allocation of a PUSCH (this is also called anuplink (UL) grant), and a set of transmit power control commands forindividual UEs within a specific UE group and/or the activation of aVoice over Internet Protocol (VoIP).

FIG. 6 is a block diagram showing a process of generating a PDCCH.

A BS determines a PDCCH format based on DCI to be transmitted to UE,attaches Cyclic Redundancy Check (CRC) to the DCI, and masks a uniqueidentifier (this is also called a Radio Network Temporary Identifier(RNTI)) to CRC depending on the owner or use of a PDCCH (510).

If the PDCCH is a PDCCH for specific UE, an identifier unique to the UE,for example, a Cell-RNTI (C-RNTI) may be masked to CRC. In analternative embodiment, if the PDCCH is a PDCCH for a paging message, apaging indication identifier, for example, a Paging-RNTI (P-RNTI) may bemasked to CRC. If the PDCCH is a PDCCH for system information, a systeminformation identifier, that is, a System Information-RNTI (SI-RNTI) maybe masked to CRC. In order to indicate a random access response, thatis, a response to the transmission of a random access preamble by UE, aRandom Access-RNTI (RA-RNTI) may be masked to CRC.

If a C-RNTI is used, a PDCCH carries control information for specific UEcorresponding to a PDCCH (this is called UE-specific controlinformation). If another RNTI is used, a PDCCH carries common controlinformation received by all UEs or a plurality of UEs within a cell.

Coded data is generated by encoding the DCI to which CRC has been added(520). The encoding include channel encoding and rate matching

The coded data is modulated, thereby generating modulation symbols(530).

The modulation symbols are mapped to a physical Resource Element (RE)(540). Each of the modulation symbols is mapped to the RE.

FIG. 7 shows an example of the resource mapping of a PDCCH.

In FIG. 7, R0 indicates the RS of a first antenna port, R1 indicates theRS of a second antenna port, R2 indicates the RS of a third antennaport, and R3 indicates the RS of a fourth antenna port.

A control region within a subframe includes a plurality of ControlChannel Elements (CCEs). The CCE is a logical allocation unit used toprovide a PDCCH with a code rate according to the status of a radiochannel, and it corresponds to a plurality of Resource Element Groups(REGs). A format of the PDCCH and the number of available bits of thePDCCH are determined depending on a correlation between the number ofCCEs and the code rate provided by the CCEs.

One REG (indicated by a quadruplet in FIG. 7) includes four REs, and oneCCE includes 9 REGs. {1, 2, 4, 8} CCEs may be used to configure onePDCCH, and each of the CCEs {1, 2, 4, 8} is called a CCE aggregationlevel.

That is, a PDCCH includes one or more CCEs, and it is mapped to physicalresources after interleaving is performed for each REG and a cyclicshift based on a cell identifier (ID) is performed.

A plurality of PDCCHs may be transmitted in one subframe. UE monitorsthe plurality of PDCCHs for each subframe. Here, the term ‘monitoring’means that the UE attempts to decode or detect the PDCCHs according to aPDCCH format.

In 3GPP LTE, blind decoding is used to detect PDCCHs. Blind decoding isalso called blind detection. Blind decoding is a method of checkingwhether a PDCCH is its own control channel by demasking a desired ID tothe CRC of a received PDCCH (this is called a candidate PDCCH) andchecking a CRC error. UE performs the blind decoding because it does notknow that its own PDCCH is transmitted using what CCE aggregation levelor what DCI format in any position within a control region.

In 3GPP LTE, in order to reduce a load resulting from blind decoding, aSearch Space (SS) is used. The search space may be called the monitoringset of CCEs for a PDCCH. UE monitors PDCCHs within a search space.

FIG. 8 is an exemplary diagram showing a common search space and aUE-specific search space for the monitoring of PDCCHs.

A search space is divided into a Common Search Space (CSS) and aUE-specific Search Space (USS). The CSS is a space where a PDCCH havingcommon control information (this is also called cell-specific controlinformation) is searched for. The CSS may include 16 CCEs from a CCEindex 0 to a CCE index 15 and supports a PDCCH having CCE aggregationlevels {4, 8}. However, a PDCCH (DCI formats 0 and 1A) that carriesUE-specific information may also be transmitted in the CSS. The USSsupports a PDCCH having CCE aggregation levels {1, 2, 4, 8}.

In a 3GPP LTE system, a PDCCH is used to control UE. A region to whichthe PDCCHs of a plurality of UEs are mapped is defined as a controlregion (or a PDCCH region). In general, a control region in which aPDCCH is transmitted is the foremost OFDM symbol period of a downlinksubframe. In general, the control region in which a PDCCH is transmittedis set within a range of ‘3 OFDM symbols’. The control region in which aPDCCH is transmitted is set to a cell-specific value owing tolimitations that all UEs have to be searched and is defined as a ControlFormat Indicator (CFI).

FIG. 9 shows an example in which a reference signal is mapped in adownlink subframe.

FIG. 9 shows an example in which a reference signal is mapped in adownlink subframe.

Various reference signals may be transmitted in a downlink subframe.

A Cell-specific Reference Signal may be received by all UEs within acell and is transmitted over all downlink bands. In FIG. 9, ‘R0’ denotesa Resource Element (RE) on which a CRS for a first antenna port istransmitted, ‘R1’ denotes an RE on which a CRS for a second antenna portis transmitted, ‘R2’ denotes an RE on which a CRS for a third antennaport is transmitted, and ‘R3’ denotes an RE on which a CRS for a fourthantenna port is transmitted.

An RS sequence r_(l,ns)(m) for a CSR may be defined as follows.

$\begin{matrix}{{r_{l,{n\; s}}(m)} = {{\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {2m} \right)}}} \right)} + {j\frac{1}{\sqrt{2}}\left( {1 - {2 \cdot {c\left( {{2m} + 1} \right)}}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, m=0,1, . . . , 2N_(maxRB)−1, N_(maxRB) a maximum numberof an RB, ns is a slot number within a radio frame, and l is an OFDMsymbol number within a slot.

A pseudo-random sequence c(i) may be defined by the Gold sequence of alength 31 below.c(n)=(x ₁(n+Nc)+x ₂(n+Nc))mod 2x ₁(n|31)=(x ₁(n|3)|x ₁(n))mod 2x ₂(n|31)=(x ₂(n|3)|x ₂(n|2)|x ₂(n|1)·x ₂(n))mod 2  [Equation 2]

In Equation 2, Nc=1600, and a first m-sequence is initialized tox₁(0)=1, x₁(n)=0, m=1,2, . . . , 30.

A second m-sequence is initialized toc_(init)=2¹⁰(7(ns+1)+l+1)(2N^(cell) _(ID)+1)+2N^(cell) _(ID)+N_(CP) atthe beginning of each OFDM symbol. N^(cell) _(ID) denotes the PhysicalCell Identity (PCI) of a cell. N_(CP)=1 in a normal CP, and N_(CP)=0 inan extended CP.

Furthermore, a UE-specific Reference Signal (URS) is transmitted in adownlink subframe. The CRS is transmitted all regions of a downlinksubframe, whereas the URS is transmitted within the data region of adownlink subframe and is used to demodulate a relevant PDSCH. In FIG. 9,‘R5’ indicates an RE on which a URS is transmitted. The URS is alsocalled a Dedicated Reference Signal (DRS) or a demodulation referencesignal (DM-RS).

The URS is transmitted only in a RB to which a relevant PDSCH is mapped.In FIG. 9, R5 is also indicated in regions other than regions wherePDSCHs are transmitted. Here, R5 indicated in the regions other than theregions where the PDSCHs are transmitted indicates the position of an REto which the URS is mapped.

The URS is used by only UE that receives a relevant PDSCH. An RSsequence r_(ns)(m) for the URS is the same as Equation 1. Here, m=0,1, .. . , 12N_(PDSCH,RB)−1, and N_(PDSCH,RB) is the number of RBs forrelevant PDSCH transmission. A pseudo-random sequence generator isinitialized to c_(init)=(floor(ns/2)+1)(2N^(cell) _(ID)+1)2¹⁶+n_(RNTI)at the beginning of each subframe. n_(RNTI) is the ID of UE.

The above example corresponds to the case where the URS is transmittedthrough a single antenna. When the URS is transmitted through multipleantennas, a pseudo-random sequence generator is reset toc_(init)=(floor(ns/2)+1)(2N^(cell) _(ID)+1)2¹⁶+n_(SCID) at the beginningof each subframe. n_(SCID) is a parameter which is obtained from a DLgrant (e.g., DCI format 2B or 2C) related to PDSCH transmission.

FIG. 10 shows an example in which information about the size of a PDCCHis received using a PCFICH.

Referring to FIG. 10, a CFI is transmitted through a PCFICH, and itcontains information about the OFDM symbol period of a control region.For example, if a CFI is 3 as in FIG. 10, a control region where UE hasto detects its own PDCCH includes 3 OFDM symbol periods. The UE obtainsits own data channels (i.e., a PDSCH/PUSCH) through the PDCCH detectedin the control region.

Meanwhile, in LTE Rel. 10, in order for a BS to send control informationabout a Relay Node (RN), an R-PDCCH has been newly designed.

FIG. 11 shows an example of the R-PDCCH.

Referring to FIG. 11, the R-PDCCH may be placed in the first slot orsecond slot of one subframe. If the R-PDCCH is placed in the first slot,a downlink grant (i.e., PDSCH scheduling information) is provided to anRN through the R-PDCCH. If the R-PDCCH is placed in the second slot, anuplink grant (i.e., PUSCH scheduling information) is provided to an RNthrough the R-PDCCH.

A position where a potential R-PDCCH is transmitted in the frequencydomain is signalized to an RN through RRC for each RB or Resource BlockGroup (RBG) depending on a resource allocation type. That is, one ormore RBs are semi-statically configured as a potential frequency domainfor R-PDCCH transmission. In a region where the potential R-PDCCH istransmitted (hereinafter referred to as an ‘R-PDCCH region’), aplurality of R-PDCCHs may be multiplexed in order to send controlinformation about different RNs.

The R-PDCCH region has the same position in the frequency domain in thefirst slot and the second slot of a subframe, but an R-PDCCH transmittedto a specific RN does not need to be always placed in the same frequencydomain in the first slot and the second slot. That is, a downlink grantand an uplink grant transmitted to a specific RN may be transmitted indifferent frequency domains.

A method of multiplexing a plurality of R-PDCCHs chiefly includes twomethods. The first method is to cross-interleave R-PDCCHs, and thesecond method is not to cross-interleave R-PDCCHs.

The first method complies with an operation in a legacy PDCCH. That is,one DCI is mapped to 1 to 8 Control Channel Elements (CCEs) depending onan aggregation level, and a plurality of the mapped DCIs iscross-interleaved in an REG unit including four contiguous ResourceElements (REs). If this method is used, a plurality of R-PDCCHs is mixedwithin one RB.

In the second method, each DCI is rate-matched with all the REs of thefirst or the second slot in 1 to 8 RBs depending on an aggregation levelafter experiencing a process of adding CRC and a channel coding process.

In case of the first method, UE receives an R-PDCCH by using aCell-specific RS (CRS) (antenna ports 0 to 3) because a plurality ofR-PDCCHs is mixed within one Physical RB (PRB). In case of the secondmethod, UE may receive an R-PDCCH by using a demodulation RS (DM-RS)(using only antenna ports 7 to 10) as well as a CRS because there isonly one R-PDCCH within one PRB.

In order to receive a downlink signal, such as a PDCCH or a PDSCH, froma BS, an RN configures a subframe on which the downlink signal will bereceived as a Multicast Broadcast Single Frequency Network (MBSFN)subframe for UE within an RN cell (hereinafter referred to as RN UE).Since the MBSFN subframe does not include a Physical Multicast channel(PMCH), RN UEs receive the PDCCH only during the first 2 OFDM symbolperiods of the MBSFN subframe, but do not receive a signal during theremaining periods. Accordingly, the RN receives the R-PDCCH and thePDSCH by using the durations where the RN UEs do not receive a signal.The RN has to send the PDCCH to the RN UEs and to receive a signal fromthe BS during the first one to two OFDM symbol periods of a relevantsubframe. In this case, a switching time is necessary between thetransmission and the reception. With consideration taken of theswitching time, the RN may receive a signal from the fourth OFDM symbolof the BS. Consequently, signals (i.e., an R-PDCCH and a PDSCH)transmitted from the BS to the RN are unconditionally transmitted fromthe position of the fourth OFDM symbol in the first slot of the subframeas in FIG. 10. In the frequency domain where there is an R-PDCCH or aPDSCH for the RN, there may be a Guard Time (GT) where a signal is nottransmitted as in FIG. 10.

Information about a subframe configuration for an RN may be transmittedthrough a Radio Resource Control (RRC) message. The following message isan example of the RRC message.

-- ASN1START RN-SubframeConfig-r10 ::= SEQUENCE { frameStructureType-r10 CHOICE {   fdd-r10   FDD-SubframeConfig-r10,  tdd-r10   TDD-SubframeConfig-r10  },  rpdcch-Config-r10 SEQUENCE {  resourceAllocationType-r10  ENUMERATED {type0, type1, type2Localized,type2Distributed},   resourceBlockAssignment-r10   CHOICE {   type01-r10    CHOICE {     nrb6-r10     BIT STRING (SIZE(6)),    nrb15-r10     BIT STRING (SIZE(8)),     nrb25-r10     BIT STRING(SIZE(13)),     nrb50-r10     BIT STRING (SIZE(17)),     nrb75-r10    BIT STRING (SIZE(19)),     nrb100-r10      BIT STRING (SIZE(25))   },    type2-r10    CHOICE {     nrb6-r10     BIT STRING (SIZE(5)),    nrb15-r10     BIT STRING (SIZE(7)),     nrb25-r10     BIT STRING(SIZE(9)),     nrb50-r10     BIT STRING (SIZE(11)),     nrb75-r10    BIT STRING (SIZE(12)),     nrb100-r10      BIT STRING (SIZE(13))   }   }_(:)   demodulationRS-r10  CHOICE {    interleaving-r10 ENUMERATED {crs}_(:)    noInterleaving-r10   ENUMERATED {crs, dmrs}  }_(:)   pdsch-Start-r10  INTEGER (1..3),   pucch-Config-r10  SEQUENCE{    n1-PUCCH-AN-port0-r10   INTEGER (0..2047),    n1-PUCCH-AN-port1-r10  INTEGER (0..2047)   }_(:)   ...  } OPTIONAL, -- Need ON  ... }FDD-SubframeConfig-r10 ::=  SEQUENCE { subframeConfigurationPatternFDD-r10   BIT STRING (SIZE(8)) }TDD-SubframeConfig-r10 ::=  SEQUENCE { subframeConfigurationPatternTDD-r10   INTEGER (0..31) } -- ASN1STOP

Meanwhile, in system higher than 3GPP LTE Rel-11, in order to improveperformance, a multi-node system including a plurality of nodes within acell is expected to be introduced. Furthermore, a standardization taskfor applying various MIMO schemes and cooperation communication schemeswhich are being developed or will be applied in the future to amulti-node environment is in progress. When a node is introduced, linkquality is expected to be improved because various communicationschemes, such as a cooperation method, can be used. However, in order toapply the various MIMO schemes and cooperation communication schemes tothe multi-node environment, there is an urgent need to introduce a newcontrol channel. For this reason, the control channel that will be newlyintroduced is an Enhanced-Physical Downlink Control Channel (E-PDCCH)(it may also be called another terminology, such as an RRH-PDCCH or anx-PDCCH, but is hereinafter referred to as an E-PDCCH). In the E-PDCCH,not the existing control region (hereinafter referred to as a PDCCHregion), but a data transport region (hereinafter referred to as a PDSCHregion) is preferred as an allocation position. A problem that theexisting PDCCH region may be insufficient can be solved because controlinformation about a node can be transmitted to each UE through theE-PDCCH.

FIG. 12 shows an example in which E-PDCCHs are allocated and an exampleof scheduling through the E-PDCCHs.

An E-PDCCH is not provided to the existing LTE Rel 8-10 UEs, but may besearched for by UE of Rel-11 or higher and some region of a PDSCH may beallocated and used. For example, a part of the PDSCH region where datais transmitted may be defined as used as an E-PDCCH as in FIG. 12.

The E-PDCCH is similar to an R-PDCCH in that it is a control channelwhere the PDSCH transport region is placed and reception is possibleusing a URS(DM-RS). A difference between the E-PDCCH and the R-PDCCHlies in that the subject of reception is UE in the E-PDCCH and thesubject of reception is an RN in the R-PDCCH.

UE has to perform a blind decoding process of detecting whether its ownE-PDCCH exists or not. If the number of UEs that haves accessed to anode is increased, however, the number of times of blind decoding thatmust be performed by the UEs is increased because more E-PDCCHs areallocated within a PDSCH region, with the result that complexity may beincreased.

The present invention is hereinafter described. In the presentinvention, in order to minimize an impact due to a change of theexisting standard rules, an E-PDCCH structure is provided while reusingthe R-PDCCH structure to a maximum and an E-PCFICH structure needed inan E-PDCCH is provided.

As described above, information about the size and position of theR-PDCCH is transferred to an RN through an RRC message. That is, theinformation about the size and position of the R-PDCCH issemi-statically provided to the RN. A channel environment is staticbecause there are RNs equal to the number of RNs determined in a fixedposition within a cell and also a probability that the amount of controlinformation will be instantly greatly changed is low. Accordingly,semi-static scheduling may be effective. However, the E-PDCCH is acontrol channel from a BS to UE having mobility. Accordingly, a channelenvironment may be dynamically changed, and the number of UEs that mustbe provided with service by a BS may be frequently changed. As a result,the amount of control information that must be transmitted by the BS mayalso be instantly changed. For this reason, there is a need for anE-PCFICH, that is, a dedicated channel for informing UE of the size andnumber of E-PDCCHs that are dynamically changed.

1. E-PDCCH Region

The E-PDCCH region refers to a region where a BS or a node may send anE-PDCCH. From a standpoint of the frequency domain, the E-PDCCH mayexist in a specific frequency domain, such as an R-PDCCH, for example, aspecific region scheduled in the unit of an RB. In the presentinvention, the E-PDCCH region may be determined in a cell-specific wayor a node-specific way. The meaning that the E-PDCCH region isdetermined in a cell-specific way means that an E-PDCCH is transmittedby using a common resource region in all nodes within a cell. Themeaning that the E-PDCCH region is determined in a node-specific waymeans that an E-PDCCH is transmitted by using a resource regiondetermined for each node within a cell.

A PDCCH region is placed within a maximum of former four OFDM symbol ofa subframe, whereas the E-PDCCH region may be flexibly scheduled withina data region.

In the PDCCH region, a PDCCH may be demodulated based on a CRS. In theE-PDCCH region, an E-PDCCH may be demodulated based on a URS. A URS maybe transmitted in a relevant E-PDCCH region.

In the E-PDCCH region, an E-PDDCH may be monitored using blind decoding.The E-PDCCH region may be monitored by one UE, a group of UEs, or UEswithin a cell. If specific UE monitors the E-PDCCH region, n_(RNTI) orn_(SCID) used to reset the pseudo-random sequence generator of an URSmay be obtained based on the ID of the specific UE. If a group of UEsmonitors the E-PDCCH region, n_(RNTI) or n_(SCID) used to reset thepseudo-random sequence generator of a URS may be obtained based on theID of the group of UEs.

When the E-PDCCH region is transmitted through multiple antennas, thesame precoding as that of the URS may be applied to the E-PDCCH region.

FIG. 13 shows an example of a node-specific E-PDCCH region.

Referring to FIG. 13, an E-PDCCH region 1 where an RRH 1 may send anE-PDCCH and an E-PDCCH region 2 where an RRH 2 may send an E-PDCCH areallocated to different RBs. From a viewpoint of the time domain, theE-PDCCH region may exist in both the first and the second slots of asubframe like the R-PDCCH, or may exist only in the first slot of thesubframe.

As shown in FIG. 13, in the present invention, different E-PDCCH regionsare subject to Frequency Division Multiplexing (FDM) and allocated foreach node. UE may detect its own E-PDCCH in an E-PDCCH region for a nodefrom which a signal will be received through blind decoding.

FIG. 13 illustrates only the E-PDCCH regions for two nodes, but notlimited thereto. In general, UE that will receive a PDSCH from an RRH ndetects its own E-PDCCH in an E-PDCCH region corresponding to the RRH nthrough blind decoding.

In order for UE to detect a target E-PDCCH within an E-PDCCH region, asize in the frequency domain of the E-PDCCH region, for example,information about the number of RBs is necessary. This is because theE-PDCCH region may be dynamically changed depending on the number of UEsand the amount of traffic.

In the present invention, the E-PCFICH provides UE with informationabout the size of an E-PDCCH region (i.e., the number of RBs) which isdynamically changed (e.g. for each subframe). The position of theE-PCFICH may be changed statically or semi-statically. UE receives anE-PCFICH placed in a designated position within each subframe andobtains information about the size of the E-PDCCH region from thereceived E-PCFICH.

2. E-PCFICH

The E-PCFICH provides UE with an E-CFI, that is, instant sizeinformation (i.e., the number of RBs) in the frequency domain of anE-PDCCH region. If there are a number of E-PDCCH regions within a cell(e.g. node-specific E-PDCCH regions), one E-CFI may include informationabout the size of one E-PDCCH region or a plurality of E-PDCCH regions.In a system including a plurality of E-PDCCH regions, only one E-PCFICHmay exist or a plurality of E-PCFICH regions (e.g., one E-PCFICH for oneE-PDCCH region) may exist.

A method of configuring the E-CFI may include 1) a method of configuringinformation about the size of a plurality of E-PDCCH regions (i.e., thenumber of RBs) as one E-CFI and 2) a method of configuring informationabout the size of each E-PDCCH region (i.e., the number of RBs) as adifferent E-CFI.

In case of 1) method, the E-CFI may configure information about the sizeof a plurality of E-PDCCH regions as one Information Element (IE). Thefollowing table is an example of information about the size of aplurality of E-PDCCH regions using one IE. In Table 1, Q may be a valuedetermined depending on a system band.

TABLE 1 E-CFI Meaning 0 No E-PDCCH regions exist. 1 All E-PDCCII regionsare Q RB sized. 2 All E-PDCCH regions are 2Q RB sized. 3 Odd numberedE-PDCCH regions are Q RB sized, and even numbered E- PDCCH regions are2Q RB sized. 4 Odd numbered E-PDCCH regions are 2Q RB sized, and evennumbered E- PDCCH regions are Q RB sized.

As shown in Table 1, the size of the E-PDCCH region may be defined asone E-CFI. For example, as shown in Table 1, if a value of the E-CFI is1, all E-PDCCH regions may be formed of Q RBs, and if a value of theE-CFI is 3, odd-numbered E-PDCCH regions of E-PDCCH regions may beformed of Q RBs and even-numbered E-PDCCH regions of E-PDCCH regions maybe formed of Q RBs.

In case of 2) method, each E-CFI indicates information about the size ofa relevant E-PDCCH region and it may be transmitted through differentphysical resources (Resource Element (RE)). Here, physical resourcesthat transfer different E-CFIs may be combined to form one E-PCFICH, ora channel that transfers each E-CFI may form an additional E-PCFICH(e.g. an E-PCFICH for each E-PDCCH region). That is, the former is amethod of sending a plurality of E-CFIs (e.g., an E-CFI #1 for anE-PDCCH region #1, an E-CFI #2 for an E-PDCCH region #2, . . . ) in oneE-PCFICH, and the latter is a method of sending only one E-CFI in oneE-PCFICH. In case of the former, a plurality of E-CFIs may be connectedto form one bitmap form. For example, if bit information transmittedthrough an E-PCFICH has a form [xxyyzz], xx may be defined to indicatean E-CFI for an E-PDCCH region #1, yy may be defined to indicate anE-CFI for an E-PDCCH region #2, and zz may be defined to indicate anE-CFI for an E-PDCCH region #3.

The position of the E-PCFICH may be previously determined or may besemi-statically configured for UE through a high layer signal, such asan RRC message.

If the position of the E-PCFICH is previously determined, the positionof the E-PCFICH may be determined by one or more parameters, such as asystem band, a cell-ID, and a node-ID (when a different CSI-RS istransmitted for each node, the node ID may be replaced with a CSI-RSconfiguration number, a CSI-RS subframe configuration number, or an RSport number).

If the position of the E-PCFICH is determined through a high layersignal, such as an RRC message, the position of the E-PCFICH may bedetermined by using i) a method of including information about theposition of the E-PCFICH in scheduling information according to aresource allocation type transmitted through the RRC message and sendingthe scheduling information and ii) a method of defining a candidateregion where an E-PCFICH may be placed, including a position index for aregion where the E-PCFICH is actually transmitted in the RRC message,and sending the RRC message.

A position relationship between an E-PCFICH and an E-PDCCH region isdescribed below.

An E-CFI includes only information about the size of an E-PDCCH region(e.g., the number of RBs). In order for UE to know that E-PDCCH regionsequal to what RBs exist based on what position, the reference positionof the E-PDCCH region must be defined. For example, assuming that anE-PDCCH region exists from a Virtual RB (VRB) #M to a VRB # (M+L) whichare contiguous to each other, it is necessary to define M because anE-CFI signalizes only L. In this example, M is a value indicating thereference position of the E-PDCCH region.

3. Position in the Frequency Domain of an E-PCFICH

An E-PCFICH may be placed in an RB region where an E-PDCCH region may beplaced in the frequency domain, that is, in some region defined from apotential E-PDCCH region. For example, the E-PCFICH may be placed in thefirst Virtual Resource Block (VRB) of the potential E-PDCCH region.

As described above, if the position in the frequency domain of theE-PCFICH is limited to the RBs of the E-PDCCH region and the position ofthe E-PCFICH is operated in conjunction with the position from thefrequency of the E-PDCCH region, there is an advantage in that signalingoverhead is reduced because UE can induce the remaining positions fromany one of the positions of the E-PCFICH and the E-PDCCH region.Furthermore, if an E-PCFICH is placed behind a PDCCH (within a PDSCHregion) on the time side, it is difficult to allocate an RB including anE-PCFICH to a legacy UE because the legacy UE does not recognize theE-PCFICH. From this point of view, if an RB where an E-PCFICH istransmitted is placed within the RB of an E-PDCCH region, there is anadvantage in that scheduling limitations to legacy UE is reduced ascompared with the case where the E-PCFICH does not overlap with the RBof the E-PDCCH region.

FIG. 14 shows an example in which an E-PCFICH is placed in RBs that forman E-PDCCH region.

For example, assuming that a potential E-PDCCH region exists from a VRB#M to a VRB # (M+L_(max)), an E-PCFICH may be defined to exist from theVRB #M to a VRB #M+c. Here, c may be a constant smaller than L_(max) andmay be a predetermined value. That is, the size of the E-PCFICH may besmaller than that of the E-PDCCH region in the frequency domain and maybe fixed.

FIG. 15 shows an example in which an E-PCFICH is placed in some resourceelements within RBs that form an E-PDCCH region.

When there is a plurality of E-PDCCH regions, a plurality of E-PCFICHmay be multiplexed within an RB forming a specific E-PDCCH region, asshown in FIG. 15. That is, an E-PCFICH does not exist within a specificRB of all E-PDCCH regions, but a plurality of E-PCFICHs exists onlywithin a specific RB of a specific E-PDCCH region. Each of the E-PCFICHsprovides information about the size of the frequency domain for arelevant E-PDCCH region.

If a plurality of E-PCFICHs is multiplexed within RBs that form aspecific E-PDCCH region, the reference position of each E-PDCCH regionmay be previously designated instead of the position of the E-PCFICH, orUE may be informed of the reference position of each E-PDCCH regionthrough a high layer signal, such as an RRC message. Furthermore, theE-PCFICH may be defined to exist in a designated position of a specificone of the plurality of E-PDCCH regions. UE receives E-CFIs fromE-PCFICHs existing in the agreed RE or RB of the specific E-PDCCH regionand obtains information about the size of the E-PDCCH regions from thereceived E-CFIs.

4. Position in the Time Domain of an E-PCFICH

An E-PCFICH may exist between the last symbol of a PDCCH and the startsymbol of an E-PDCCH region in the time domain. This has advantages fromtwo points of views. The first advantage is that processing delay can beminimized by placing an E-PCFICH in front of an E-PDCCH because thedetection order of UE within a subframe is the E-PCFICH, the E-PDCCH,and a PDSCH. The second advantage is that a shock due to a change of therules can be minimized because the frame structure of the E-PDCCH mayalmost comply with the frame structure of the R-PDCCH.

An R-PDCCH is placed in all REs of an RB determined in the frequencydomain, and it may exist in i) the fourth to seventh OFDM symbols of afirst slot, ii) the first to seventh OFDM symbols of a second slot, oriii) the first to sixth OFDM symbols of the second slot in the timedomain. In accordance with the present invention, the two types ofconfigurations i) and ii) from among the three types of configurationsof the R-PDCCH may be reused to design an E-PDCCH. The configurationiii) may not be used in the E-PDCCH when the switching time of an RN istaken into consideration.

How the position of an E-PCFICH will be configured depending on thestart position of an E-PDCCH region when the E-PCFICH exists isdescribed below.

1) The Position of an E-PCFICH When the Start Symbol of an E-PDCCH isFixed

If an E-PDCCH exists in the first slot of a subframe, a BS may send theE-PDCCH from a fixed position, that is, the fourth OFDM symbol of thesubframe (a symbol index value is 3). Here, the E-PCFICH may existduring one or two symbol periods between the PDCCH region and theE-PDCCH region in the time domain. The start position of the E-PCFICHmay follow one of the following.

i) A Control Format Indicator (CFI)+the First OFDM Symbol

This is a method in which the position of an E-PCFICH is dynamicallychanged according to a CFI. That is, a PDCCH region is dynamicallychanged over first to third OFDM symbol periods for each subframeaccording to the CFI. Here, the E-PCFICH exists right after the PDCCHregion, that is, during one to two symbol periods from the second tofourth OFDM symbols of the subframe. In this case, the CFI may belimited so that it has only 1 or 2 because the E-PDCCH region existsfrom the fourth OFDM symbol. That is, the case where the CFI has a valueof 3 is excluded. In summary, the three cases of Table 2 below may besupported.

TABLE 2 Symbol index(es) Symbol index(es) E-PDCCH CFI for PDCCH forE-PCFICH start symbol 1 0 1 3 1 0 1, 2 3 2 0, 1 2 3

Table 2 indicates OFDM symbol indices in the time domain of a PDCCHregion, an E-PCFICH, and an E-PDCCH region according to a CFI (the indexis started from 0). In Table 2, when CFI=1, two cases are possibledepending on the number of transmission symbols of an E-PCFICH. Whichone of the two cases will be used may be previously determined between aBS and UE or a BS may inform UE of it through a high layer signal. Forexample, if an E-PCFICH has been defined so that it is unconditionallytransmitted for one symbol period, the second case of Table 2 isexcluded.

ii) Fixed so that the Position of the E-PCFICH is Stared from a ThirdOFDM Symbol

The E-PCFICH is defined as always existing in the position of the thirdOFDM symbol irrespective of a CFI. Even in this case, CFI=3 may belimited for the transmission of the E-PCFICH. In case of the method i),UE may know the position of the E-PCFICH in the time domain only whenthe UE recognizes a CFI through a PCFICH. In contrast, in case of themethod ii), UE may know the position of the E-PCFICH in the time domainalthough the UE does not receive a CF. If the method ii) is applied, thefollowing two cases as in Table 3 may be supported.

TABLE 3 Symbol index(es) Symbol index(es) E-PDCCH CFI for PDCCH forE-PCFICH start symbol 1 0 2 3 2 0, 1 2 3

In the above-described method, the frame structure of the E-PDCCH isidentical with the frame structure of the R-PDCCH. This method isadvantageous in that a shock due to a change of the rules can beminimized, but is disadvantageous in terms of resource efficiency. Inparticular, if CFI=1 and the transport period of an E-PCFICH is definedto be one OFDM symbol, there is a disadvantage in that one symbol isempty between the PDCCH, the E-PCFICH, and the E-PDCCH as can be seenfrom Table 2 and Table 3. In order to maximize resource efficiency, itis preferred that the start symbol of an E-PDCCH be flexibly operateddepending on a CFI. The following method may be used by taking theflexible operation of the start symbol of the E-PDCCH intoconsideration.

2) The Position of an E-PCFICH When the Start Symbol of an E-PDCCH isFlexible

If the start symbol of an E-PDCCH is not fixed to the fourth OFDM symbolof a subframe, but may be flexibly changed, an E-PCFICH may exist duringone or two symbols from a CFI+the first OFDM symbol, and the E-PDCCH mayexist from a symbol right after the E-PCFICH.

Assuming that the number of transmission symbols is N in the time domainof an E-PCFICH, the E-PCFICH and an E-PDCCH region may be configured asin Table 4. Here, the number N of transmission symbols of the E-PCFICHmay be previously defined (e.g., previously defined as N=1), or UE maybe informed of the number N of transmission symbols through a high layersignal, such as an RRC message.

TABLE 4 Symbol index(es) Symbol index(es) E-PDCCH CFI for PDCCH forE-PCFICH start symbol 1 0 1, . . . , N N + 1 2 0, 1 2, . . . , N + 1 N +2 3 0, 1, 2 3, . . . , N + 2 N + 3

In accordance with a method, such as that of Table 4, there aredisadvantages in that the standard rules need to be changed and a CFImust be received from a PCFICH in order to receive an E-PDCCH. However,there is an advantage in terms of resource efficiency because the startsymbol of an E-PDCCH region is operated in conjunction with a CFI.

Hereinafter, a method of signalizing the reference position of anE-PCFICH or an E-PDCCH region when there is a plurality of E-PDCCHregions within a subframe is described. Here, the reference positiondenotes a resource (e.g., an RB) in the frequency axis where eachE-PDCCH region or each E-PCFICH region is started.

For example, it is assumed that an E-PDCCH region #0 to an E-PDCCHregion #N exist within a subframe. If a BS sends all reference positionsfor the E-PDCCH region #0 to the E-PDCCH region #N, respectively, to UE,signaling overhead may be great. In particular, when an N value isgreat, signaling overhead may become problematic.

In order to solve this problem, in the present invention, UE is informedof only a reference position for one E-PDCCH region which is areference, from among a plurality of E-PDCCH regions, and referencepositions for the remaining E-PDCCH regions may be implicitly determinedbased on the informed reference position.

For example, it is assumed that an E-PDCCH region #0 is set in#m(0)+Lmax−1 from a VRB #m(0). Here, m(0) is the reference position ofthe E-PDCCH region #0, and Lmax is a maximum number of RBs that may beowned by the E-PDCCH region #0. Furthermore, the reference position ofan E-PDCCH region #n (n is a natural number greater than 1) is indicatedby m(n). Here, m(n) may be regulated by a function of m(0). For example,m(n)=m(0)+n·Lmax may be regulated. If this regulation is previouslyagreed between a BS and UE, the UE can know reference positions for theremaining E-PDCCH regions although only m(0), that is, the referenceposition of the E-PDCCH region #0, is received. A BS may inform UE of areference position for a plurality of E-PDCCH regions using this method.

Furthermore, in the above example, a BS and UE may previously agreedthat each E-PDCCH region is allocated to consecutive VRBs andneighboring E-PDCCH regions are contiguous to each other. In this case,if the BS informs the UE of m(0) and an Lmax value for the E-PDCCHregion #0, the UE may also know the size of other E-PDCCH regions. Thatis, it can be seen that the E-PDCCH region #1 is allocated to#m(0)+2Lmax−1 from VRB #m(0)+Lmax. It can be seen that the E-PDCCHregion #2 is allocated to #m(0)+3Lmax−1 from VRB #m(0)+2Lmax.

For another example, it may be previously determined that the E-PDCCHregion #n shifts RBs or RB groups to which the E-PDCCH region #0 hasbeen allocated by n RB. For example, it is assumed that the E-PDCCHregion #0 is placed in RB groups indicated by a bitmap 101000, fromamong 6 RB groups. That is, it is assumed that the E-PDCCH region #0 isplaced in the first RB group and the third RB group. Here, the E-PDCCHregion #1 may be placed in RB groups indicated by a bitmap 010100, andthe E-PDCCH region #2 may be placed in RB groups indicated by a bitmap001010. That is, another E-PDCCH region is configured by shifting RBgroups, forming an E-PDCCH region that is a reference, by 1 RB group. Ifthis regulation is known to both a BS and UE in advance, when the BSinforms the UE of only the reference position of the E-PDCCH region #0,the UE may know reference positions for other E-PDCCH regions.

In the above examples, a reference position for E-PDCCH regions has beendescribed, but the examples may also be applied to the signaling of areference position for an E-PCFICH region.

For example, if an E-PCFICH is allocated to two RBs based on thereference position of an E-PDCCH region in the frequency domain as inFIG. 14, an E-PCFICH #0 may be allocated to VRB #m(0) and #m(0)+1, anE-PCFICH #1 may be allocated to VRB #m(0)+Lmax and #m(0)+Lmax+1, and anE-PCFICH #2 may be allocated to VRB #m(0)+2Lmax and #m(0)+2Lmax+1. Here,a BS may inform UE of only the reference position of an E-PCFICH (e.g.,the E-PCFICH #0) that is a reference. Accordingly, the UE may know thereference position of each E-PCFICH.

Meanwhile, a plurality of E-PCFICHs may be multiplexed within one RB asshown in FIG. 15. In this case, it may be difficult to signalize thereference position of each E-PCFICH or the reference position of aspecific E-PCFICH for each RB. This is because it may be difficult todistinguish the E-PCFICHs from each other although each E-PCFICH existsin only some REs within the RB in the frequency axis and informs thereference position for each RB. In this case, the BS may signalizeinformation about the reference position and/or size of each RB wherethe plurality of E-PCFICHs exists (e.g., information indicating that oneE-PCFICH consists of how many REs or REGs).

If the number and position of REs (or REGs) to which each E-PCFICH maybe allocated are determined by the number of E-PCFICHs existing in oneRB, the information about the size of the RB may not be signalized, andinstead information about the total number of E-PCFICHs may besignalized.

For example, it is assumed that an E-PCFICH region includes N (N is oneof 1 to 3) RBs in the frequency axis and the third OFDM symbol of afirst slot in the time axis and N E-PCFICHs are allocated within theE-PCFICH region. In this case, the E-PCFICH region may use 12 REs (or, 3REGs) per RB. Here, the N E-PCFICHs may be multiplexed or interleaved asfollows.

If there is only one E-PCFICH within the E-PCFICH region, all the 3 REGsof one RB are allocated to the one E-PCFICH.

If there are two E-PCFICHs, REGs #1, 3, and 5 of a total of 6 REGs areallocated to the E-PCFICH #0 and REGs #0, 2 and 6 are allocated to theE-PCFICH #1.

If there are three E-PCFICHs, an E-PCFICH #0 is allocated to the 1^(st),4^(th), and 7^(th) REGs (i.e., the first REGs of respective RBs) of atotal of 9 REGs of three RBs, an E-PCFICH #1 is allocated to 2^(nd),5^(th), and 8^(th) REGs (i.e., the second REGs of the respective RBs)thereof, and an E-PCFICH #2 is allocated to the 3^(rd), 6^(th), and9^(th) REGs (i.e., the third REGs of the respective RBs) thereof. In theabove example, although the case where N is a maximum of 3 has beendescribed, this method may also be extended to the case where N is 4 orhigher. The above-described multiplexing or interleaving method is onlyillustrative, and other predetermined methods may be used.

If a BS and UE knows the multiplexing or interleaving method ofE-PCFICHs in advance, the BS may inform the UE of information about thereference position of an E-PCFICH region to which a plurality ofE-PCFICHs may be allocated and information about the total number ofactually allocated E-PCFICHs. For example, the BS may inform the UE ofonly the reference position of an RB where E-PCFICHs exist and the totalnumber of the E-PCFICHs semi-statically through a higher layer signal.Accordingly, the UE may know a reference position where each of theE-PCFICHs is placed.

FIG. 16 shows a method of UE monitoring a control channel according toan embodiment of the present invention. Two E-PCFICHs and two E-PDCCHsare described as an example, for convenience of description, but thepresent invention is not limited thereto.

Referring to FIG. 16, the UE obtains information about the referenceposition of a first E-PCFICH and the total number of E-PCFICHs through ahigher layer message at step S401. The higher layer message may be anRRC message. That is, information about the reference position of thefirst E-PCFICH may be semi-statically set.

The UE obtains the reference position of a second E-PCFICH based on theinformation about the reference position of the first E-PCFICH at stepS402. That is, the information about the reference position of thesecond E-PCFICH may be extracted based on the information about thereference position of the first E-PCFICH.

The UE obtains the frequency size of a first E-PDCCH region through thefirst E-PCFICH and obtains the frequency size of a second E-PDCCH regionthrough the second E-PCFICH at step S403.

The UE performs blind decoding in order to detect control informationallocated thereto in the first E-PDCCH region and the second E-PDCCHregion and receives a downlink signal or send an uplink signal when itsown control information is detected.

Although not shown in FIG. 16, in the method, a BS may inform the UE ofonly the reference position of the first E-PDCCH region. Thus, the UEmay derive the reference position of the second E-PDCCH region based onthe reference position of the first E-PDCCH region. The UE can know thedetailed positions of the resources of the first E-PDCCH region and thesecond E-PDCCH region because it can know the reference positions of thefirst E-PDCCH region and the second E-PDCCH region and know the size onthe frequency axis of the first E-PDCCH region and the second E-PDCCHregion through the first E-PCFICH and the second E-PCFICH.

The above-described methods, the E-PCFICH, and the E-PDCCH may beapplied to not only a multi-node system, but other systems. For example,in a single node system, the above-described methods, the E-PCFICH, andthe E-PDCCH may be applied for efficient DCI transmission using a DM-RSand for an increased PDCCH capacity. Furthermore, when cross-carrierscheduling is applied in a carrier aggregation, a DCI for a secondarycell may be transmitted by a primary cell. In this case, in order tosolve the shortage of a PDCCH capacity in the primary cell, the E-PCFICHand the E-PDCCH proposed in the present invention may be applied.

FIG. 17 is a block diagram showing of a BS and UE.

The BS 100 includes a processor 110, memory 120, and a Radio Frequency(RF) unit 130. The processor 110 embodies the proposed functions,processes and/or methods. For example, the processor 110 sendsinformation about the reference position of an E-PCFICH region or/and anE-PDCCH region which is a reference and information about the totalnumber of E-PCFICH regions and or/and E-PDCCH regions to UE through ahigher layer signal. Furthermore, the processor 110 may send informationabout the size of the frequency domain of an E-PDCCH region through anE-PCFICH. In the E-PDCCH region, control information about each node maybe transmitted. In the E-PDCCH region, unlike a PDCCH region using aCRS, a control signal which can be demodulated through a UE-specificReference Signal (URS) is transmitted. The memory 120 is coupled to theprocessor 110 and configured to store various pieces of informationnecessary to drive the processor 110. The RF unit 130 is coupled to theprocessor 110 and configured to send and/or receive radio signals.

The UE 200 includes a processor 210, memory 220, and an RF unit 230. Theprocessor 210 implements the proposed functions, processes and/ormethods. For example, the processor 210 may obtain information about thereference position of an E-PCFICH region and/or an E-PDCCH region thatis a reference and/or information about the total number of E-PCFICHregions and/or E-PDCCH regions through a higher layer signal and mayobtain information about the size of the frequency domain of an E-PDCCHregion through an E-PCFICH. Furthermore, the processor 210 may searchthe E-PDCCH region for its own E-PDCCH through blind decoding. Thememory 220 is coupled to the processor 210 and configured to storevarious pieces of information necessary to drive the processor 210. TheRF unit 230 is coupled to the processor 210 and configured to sendand/or receive radio signals.

The processor 110, 210 may include Application-Specific IntegratedCircuits (ASICs), other chipsets, logic circuits, data processors and/ora converter for converting a baseband signal and a radio signal and thevice versa. The OFDM transmitter and the OFDM the receiver of FIG. 7 maybe implemented within the processor 110, 210. The memory 120, 220 mayinclude Read-Only Memory (ROM), Random Access Memory (RAM), flashmemory, memory cards, storage media and/or other storage devices. The RFunit 130, 230 may include one or more antennas for sending and/orreceiving radio signals. When the embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) that performs the above function. The module may be stored inthe memory 120, 220 and executed by the processor 110, 210. The memory120, 220 may be placed inside or outside the processor 110, 210 andconnected to the processor 110, 210 using a variety of well-known means.

While the invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

The invention claimed is:
 1. A method for monitoring control information in a wireless communication system, the method comprising: receiving, by a User Equipment (UE), information about a first reference position for a first Enhanced-Physical Control Format Indication Channel (E-PCFICH) from a Base Station (BS), wherein the information about the first reference position for the first E-PCFICH indicates a Resource Block (RB) where a first E-PCFICH region is started; detecting, by the UE, the first E-PCFICH in the RB indicated by the information about the first reference position for the first E-PCFICH; obtaining, by the UE, information about a second reference position for a second E-PCFICH based on the information about the first reference position, wherein the information about the second reference position for the second E-PCFICH indicates an RB where a second E-PCFICH region is started, and wherein each of the first E-PCFICH and the second E-PCFICH is a control channel comprising information about a size of a frequency domain for an Enhanced-Physical Downlink Control Channel (E-PDCCH) for demodulating control information by using a UE-specific Reference Signal (URS); detecting, by the UE, the second E-PCFICH in the RB indicated by the information about the second reference position for the second E-PCFICH; and receiving information related to a total number of a plurality of E-PCFICHs when the plurality of E-PCFICHs is multiplexed within one RB, wherein the information related to the total number of the plurality of E-PCFICHs is signaled when the plurality of E-PCFICHs is multiplexed within the one RB, wherein, when the received information indicates that one E-PCFICH is positioned within one of the E-PCFICH regions, all of three resource element groups (REGs) are allocated to the one E-PCFICH, wherein, when the received information indicates that two E-PCFICHs are positioned within one of the E-PCFICH regions, a first, a third, a fifth number of REGs are allocated to a first number of E-PCFICHs, and a second, a fourth, a sixth number of REGs are allocated to a second number of E-PCFICHs, and wherein, when the received information indicates that three E-PCFICHs are positioned within the E-PCFICH regions, a first, a fourth, a seventh number of REGs are allocated to a first number of E-PCFICHs, and a second, a fifth, an eighth number of REGs are allocated to a second number of E-PCFICHs, and a third, a sixth, an ninth number of REGs are allocated to a third number of E-PCFICHs.
 2. The method of claim 1, further comprising: obtaining a frequency size of the first E-PDCCH region through the first E-PCFICH and obtaining a frequency size of the second E-PDCCH region through the second E-PCFICH; and searching the first E-PDCCH region and the second E-PDCCH region for the E-PDCCH for the UE.
 3. The method of claim 2, further comprising: receiving information about a third reference position for the first E-PDCCH indicating the RB where the first E-PDCCH region is started.
 4. The method of claim 3, wherein the information about the third reference position for the first E-PDCCH is further used to determine the RB where the second E-PDCCH region is started.
 5. The method of claim 1, wherein the information about the first reference position is received through a higher layer signal.
 6. A User Equipment (UE) for monitoring control information in a wireless communication system, the UE comprising: a Radio Frequency (RF) unit configured to transmit and receive radio signals; and a processor connected to the RF unit, the processor being configured to: receive information about a first reference position for a first Enhanced-Physical Control Format Indication Channel (E-PCFICH) from a Base Station (BS), wherein the information about the first reference position for the first E-PCFICH indicates a Resource Block (RB) where a first E-PCFICH region is started, detect the first E-PCFICH in the RB indicated by the information about the first reference position for the first E-PCFICH, obtain information about a second reference position for a second E-PCFICH based on the information about the first reference position, wherein the information about the second reference position for the second E-PCFICH indicates an RB where a second E-PCFICH region is started, and wherein each of the first E-PCFICH and the second E-PCFICH is a control channel comprising information about a size of a frequency domain for an Enhanced-Physical Downlink Control Channel (E-PDCCH) for demodulating the control information by using a UE-specific Reference Signal (URS), detect the second E-PCFICH in the RB indicated by the information about the second reference position for the second E-PCFICH, and receive information related to a total number of a plurality of E-PCFICHs when the plurality of E-PCFICHs is multiplexed within one RB, wherein the information related to the total number of the plurality of E-PCFICHs is signaled when the plurality of E-PCFICHs is multiplexed within the one RB, wherein, when the received information indicates that one E-PCFICH is positioned within one of the E-PCFICH regions, all of three resource element groups (REGs) are allocated to the one E-PCFICH, wherein, when the received information indicates that two E-PCFICHs are positioned within one of the E-PCFICH regions, a first, a third, a fifth number of REGs are allocated to a first number of E-PCFICHs, and a second, a fourth, a sixth number of REGs are allocated to a second number of E-PCFICHs, and wherein, when the received information indicates that three E-PCFICHs are positioned within one of the E-PCFICH regions, a first, a fourth, a seventh number of REGs are allocated to a first number of E-PCFICHs, and a second, a fifth, an eighth number of REGs are allocated to a second number of E-PCFICHs, and a third, a sixth, an ninth number of REGs are allocated to a third number of E-PCFICHs.
 7. The user equipment of claim 6, wherein the processor is further configured to: obtain a frequency size of the first E-PDCCH region through the first E-PCFICH, and obtain a frequency size of the second E-PDCCH region through the second E-PCFICH, and search the first E-PDCCH region and the second E-PDCCH region for the E-PDCCH for the user equipment.
 8. The user equipment of claim 7, wherein the processor is further configured to receive information about a third reference position for the first E-PDCCH indicating the RB where the first E-PDCCH region is started.
 9. The user equipment of claim 8, wherein the information about the third reference position for the first E-PDCCH is further used to determine the RB where the second E-PDCCH region is started.
 10. The user equipment of claim 6, wherein the information about the first reference position is received through a higher layer signal. 